The present invention is related to devices for stimulating the skin in response to an external stimulus in order to aid a person who is sensorially impaired with respect to that external stimulus.
Cutaneous signaling devices which respond to sound or light, are well known aids to persons having impaired senses of hearing or sight. For example, previous auditory systems, such as that disclosed in U.S. Pat. No. 2,702,344, utilized a microphone to pick up sound which was then electrically divided into signals corresponding to various frequency bands within the audio spectrum. The magnitude of the signal for each band was employed to stimulate different regions of the skin of a hearing impaired individual. One type of such stimulation involved energizing separate electromagnetic solenoids which caused a plunger to impact the skin. With proper training the hearing impaired individual was able to recognize different sounds by the patterns of impact of the solenoid stimulator array.
Another type of stimulator employed a pattern of electrodes each having an electrical current applied to it in response to sound in a different one of the audio bands. Often such devices applied the stimulating current as a pair of pulses of opposite polarity and equal magnitude. These stimulators were current controlled so that the voltage could increase as the user's skin resistance increased. The magnitude of the current applied to a given electrode corresponded to the intensity of the sound in the respective audio band. This enabled the individual to perceive not only sound within each of the bands, but the sound's relative intensity. Similar electrode stimulation devices were created for the visually impaired individual with two dimensional stimulator arrays responding to picture elements of a video image.
The major drawback to the previous cutaneous stimulator systems was skin irritation produced after a relatively short period of usage (e.g. on the order of a few minutes). Skin reddening was quite common and even burns have been reported with the electrical stimulation. Therefore, before such cutaneous stimulators can effectively be used as an aid to a visually or hearing impaired individual, a solution to the skin irritation problem must be found to enable their continuous use for periods of practical duration.